Well- tipping increases your chance in encountering shinies, so tip away- I just encountered my first shiny (Zubat) after tipping $4,000 at the diners for leveling up pokies after needing money to buy vitamins, then went to go EV train- and after my third horde encounter was the shiny.
I am still doing research on all the "tip" info, but, as I see it for now- tipping does work-